How to Fix Bump Steer in the Dodge Challenger

Bump steer is the effect of the front wheels steering themselves without any input from the driver. Undesirable to say the least and dangerous to say the most, bump steer is a phenomenon that can occur when the steering geometry is not set up correctly and the suspension is upset due to a bump or other irregularity in the road surface.

As the suspension moves when it encounters a bump, the tire too will follow an arc up and down. Depending on the geometry of the steering and suspension, if the arc the tire travels is not the same arc as the suspension travel then the toe of the tire may be pulled in or out. Extra toe in or out can cause the tire to slightly change in direction and will consequently pull the car to follow. These steering impulses cause skittish behavior, unstable tracking and could easily lead to a crash. Even if holding the steering wheel firmly centered the entire time, bump steer can still occur. 

Mathematically speaking, bump steer is the amount of toe deflection the tire faces per inch of suspension travel. The ideal amount of bump steer is zero toe deflection for any amount of suspension travel.

In the case of the Challenger, bump steer is both a good news and a bad news situation. Starting with the good news; Dodge (as do all manufacturers) does its best to eliminate bump steer within the stock factory location. At stock ride height and suspension settings, an OEM Challenger should measure in around 0.0625 (1/16) inches of bump steer. This is very close to zero (obviously) and thus Dodge has done a good job, especially when considering the Challengers of yore (going back to the 60s and 70s) had bump steer measurements of around 0.75 inches!

The bad news regarding Challengers and bump steer is that they become susceptible to it when lowering the ride height or swapping in some coil overs. Under these conditions, the steering arc will change from that of the suspension travel and lead to bump steer.

The exact science of bump steer, tie rod, and suspension geometry is as such. Draw one line from the upper ball joint directly to the lower ball joint (let’s call it line A). Draw a second line that joins the upper control arm pivot point to the lower control arm pivot point (line B). The outer tie rod must fall somewhere on line A and the inner must fall somewhere on line B. Furthermore, the center of the tie rod must align with the center of the control arms, which can be depicted by extending a parallel line and seeing where they intersect (with each respective control arm).

Now, for a more simplistic approach.

In order to achieve zero bump steer, the tie rod must travel along the same arc (between the lower and upper control arm) that the suspension does when displaced. This means the length and angles of the tie rods play a critical role in maintaining this careful tangential relationship and lowering the ride height via springs or coil overs is sure to disrupt the OEM calculations. Thus, bump steer will rear its ugly head and something will need to be done about it. 

The aftermarket has come up with a couple of fairly easy solutions in order to deal with bump steer. Again, the most critical part of this equation is getting the tie rod to articulate along the same arc as the control arms. 

After lowering a Challenger with some drop springs, one easy method to correct the geometry and bump steer issue is to use a set of offset rack bushings. These bushings (usually polyurethane) move the steering rack a fixed amount in order to put the tie rod arc back in line with the control arms. This type of solution (inexpensive) works well for regular street-level drops of 1.5-2 inches. Of course, since the bushings move the rack a fixed amount, there is no further adjustability. Thus depending on what lowering kit you get, you cannot dial in any more bump steer correction. Also, due to their polyurethane construction, these bushings tend to firm up steering feel and reduce steering noise.

A second type of corrective kit comes in the form of adjustable outer tie rod ends. These outer tie rods can adjust via spacers and shims in order to get the tie rod back into the proper arc. While more expensive than a pair of offset rack bushings, this type of adjustable outer tie rod allows for significantly more adjustability and bump steer can really be measured and adjusted based on the actual suspension components.

Aftermarket castor/camber plates are certainly available for a Challenger, however, in the scope of bump steer they play little, if any, role. They do absolutely help with tire alignment but are not involved with toe direction as the suspension travels.

The same applies to ball joints. In the case of bump steer, there aren’t any special ball joints that can be utilized in order to reduce bump steer, at least not with the OEM control arms. That said, ball joints could play a roll if swapping to aftermarket control arms.

Theoretically speaking, aftermarket control arms could definitely affect bump steer, as, depending on how they are constructed, any change in length or mounting points could affect the arc that the tie rod needs to follow. However, if swapping a control arm is going to affect bump steer, it will be clearly annotated by the manufacturer and specific instructions will be given detailing if any other specialty parts or corrective measures are necessary.